SilverStripe PHP Forms - If I nest a SelectionGroup inside a FieldGroup, one of the related SelectionGroup_Items' Radio Box does not show up. Why?

I have a form that has two FieldGroups, and in one of the FieldGroups I have a SelectionGroup.

The SelectionGroup_Items show up in the form FieldGroup but the radio boxes to select one of the options doesn't show. If I remove the FieldGroup it then works again.

I've looked at the framework templates, and if I change the FieldGroup_holder.ss SmallFieldHolder to FieldHolder the radio boxes appear again and work correctly. I've tried following the templates to see which one isn't obeying the SelectionGroup but I keep getting lost.

Here's an example bit of code

$fields = FieldList::create(
	FieldGroup::create(
		TextField::create('Name', 'Name')
	),
	FieldGroup::create(
		SelectionGroup::create(
			'Test1or2',
			array(
				SelectionGroup_Item::create(
					'Test1', array(
						TextField::create('Test1', 'Test1')
					),
					'Test1'
				),
				SelectionGroup_Item::create(
					'Test2', array(
						TextField::create('Test2', 'Test2')
					),
					'Test2'
				)
			)
		)
	)
),
FieldList::create(
	FormAction::create('submit', 'Submit')
)

You could add another fieldset then set it's attributes to id="hidden_field" aria-hidden="true". In the css document you could do the following.

    #hidden_field{
        display:none;
        height:0;
        width:0;
        margin:0;
        padding:0;
        visibility: hidden;
    }

This should hide SilverStripe Framework's query behavior. In my own php forms I had random brackets appearing whenever someone submitted a new form numerous times under different part-id numbers. I used this approach to hide the random brackets on my site.